1. Field of the Invention
This invention relates to medical equipment and in particular to non-reusable hypodermic syringes.
2. Description of the Prior Art
If not the most widely used medical tool, the hypodermic syringe is near the top of any list on the subject. Since it has both legal and illegal uses it is important that the syringe be used correctly. It is well known that the syringe in the hands of a drug user is an instrument of the devil, not only for the injection of illegal drugs but also the spread of disease caused by reuse of the same needle. Although not generally thought of as sinister, the reuse of the syringe in cases of mass immunizations, particularly in third world countries, has at least the same potential for spreading disease but among an innocent, defenseless population.
Recently, with the introduction of AIDS into the drug formula, especially for the intravenous user, there has been a serious attempt to control the spread of the disease through the control of needles or syringes used in the process. For example, U.S. Pat. No. 4,713,056 issued Dec. 15, 1987 to Butterfield, shows a non-reusable hypodermic syringe that utilizes a lock ring (10) that is located in groove (14) of the barrel (12). As piston (16) passes the lock ring, fingers (26) deflect allowing it to move in one direction and expel the contents of the barrel, however the fingers will not allow the piston to retract and be reused. U.S. Pat. No. 4,878,899 issued Nov. 7, 1989 to Plouff discloses a disposable syringe that uses a plurality inwardly extending arms that slide over the plunger which then restrain the plunger from any further movement. In the U.S. Pat. No. 4,932,941 issued Jun. 12, 1990 to Min et al. a disposable syringe is shown that utilizes a set of inwardly directed tapered notches (5) that restrain the piston from retraction once it has travelled its full stroke and discharged its contents. The Safety Hypodermic Syringe of Tsao disclosed in U.S. Pat. No. 5,019,044 issued May 28, 1991 shows a plunger shaft having a displaceable plug (56) in alignment with a needle holder plate (34), when the shaft has travelled full stroke the plug is displaced by the plate which engages the walls of the aperture and is dislocated along with the needle as the shaft is retracted, FIGS. 3 and 4. U.S. Pat. No. 5,021,047 issued Jun. 4, 1991 to Movern is drawn to a restricted use syringe utilizing teeth on means attendant to the plunger shaft in cooperation with annular corrugations on the interior surface of the syringe wall to prevent retraction of the piston shaft.
The prior art clearly demonstrates the need for a hypodermic syringe that is safe, reliable and discourages attempts for reuse.